Pugmill



1951 E. M. SKIPPER 2,572,063

PUG MILL Filed June 6, 1947 3 Sheets-Sheet l EDWHRD "SKIPPER.

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E. M. SKIPPER PUG MILL 3 Sheets-Sheet 2 Filed June 6, 1947 3 Wu wwtov N1r A/ Enwnren r1. SKIPPER.

E. M. SKIPPER Oct. 23, 1951 PUG MILL Filed June 6, 1947 3 Sheets-Sheet 3gwu /wfm EDWHRD r1. SKIPPER.

Patented Oct. 23, 1951 :Edward SkippenrBaltimore, Md., assignor toGeneral Electric a Company, a corporation of New .York

Application'June 6, 1947, "Sel'ial NoT7 53,021

I 4 Claims. {:1

'l hisinvention relates toa pug m ill aand is a continuation-impart:of:my co-pendingapPlications, Serial" No. 4991576, "filed August- 23,1943, nowabandoned, and serial No. '708 ,455;' filed'November '7, 1946,now abandoned.

As -stated in: the aforementioned applications, manufacturers of ceramicmaterials-and particularly of porcelain insulators. have long beenconfronted: with large lossfactors in theforming and firingofceramicbodies. "Theselosses I have discovered to: be" attributable-tothe manner in which' the clayis mixed and extruded, usually in a-pugmill. -I' have round the" principal sources.

*of loss to be the lackof "homogeneity and the existence of linesofforce in the'clay-as extruded from the mill,-"for both of which Idescribed solutions' at length in my -co-pendin'g applications.

The pug mills heretofore employed for mixing ceramic materials havbeen-of two general types. In'one' the mill"=has but a s'ingle'chamberfor botli mixing and 'extruding'the material. In the other thesefunctions are performed in separate chambersfthis' typexb'eing the onemost generally used in the insulator industry. However; in both casesthe 'mixing and extruding-angers have I either-been mounted on the sameshaft or :driven through gearing at fixed relative speeds. Asresultagiven pug niill has been capable-of han- 'dling only-relatively.small variations in the consistencyor moi'stur-e contentof the startingmaterial. -Accordingly, it has beencustomary'to adapt one :mill foruse-'witl'i so-called soft" *pugs and: to use: a separate machine for"hard pu'gs. Inhave now found that by making: provision for 'both"individual and relative "variations in :the speedszattwhich: theseveralaugers' and paddles are :driven, inaconjunction :with' 'my"aforementioned discoveries:- a' single pug mill can be used topugstartmg materials oft'a wide range of con- :sistencie's.

.-.The primar object of the invention is to provide an'improvedapparatusfor producing homegeneousstress freeceramic mixtures from start- :ingmaterials-of a: vvide range of consistencies.

SAno-ther 1 object of the invention. is toprovide an: lim-provedapparatus -for pugging ceramic materials having means for varying theindividual and'relative speeds of the mixing and extruding 1 angers andmeans within the vacuum chamber "whereby? a "homogeneous pug is-obtained from i-startingzmaterials of differentconsistencies.

' :Ani'additional' object of-the invention isto p'r'o- :videanimprovedtpug mill having meansfor-constrolling? the moisture and air"content2and -elim --inating.:lines :of force'tin startingmaterials ofdii ferent consistencies "whereby the: resulting z pug :is homogeneousin' density and :moisture content and; free :fromustresses.

Other' objectsand advantages ofthe invention will :appear hereinafterin" the detailed descripition andvbeparticularly pointed outfin theappended: claims. I In the drawings illustrating -'a preferredembodiment .of the: apparatus of =1 this invention:

Eigure; 1' issa longitudinal sectional View of 'a rug 2min; embodying:my invention.

-Figuret2 is a view; partly 'in 'endel'evation and partly in sectiontaken on amen-:2orEigure 1.

Figure 3 is -a"'vertica1: sectional view taken on line13*3 of Figure 1.

Figure-4 isa side elevational view of theouter end: portion of theextruding auger.

Figure 5 is an end elevational viewer: the "extruding auger. I

Figure 6 1s a perspective-view of the outer end portion or that auger.

Figurel is a sectional "view' taken on line I--l on Figure 4. r

. Referring nowin-"=detail'- to the drawings in which like referencecharacters designat'e like parts, I indicates a suitable base onWhich'the pug mill, :designated generally as- 2, "is' mounted.

Theimixingportionof thepu'g rnill comprises a 'hoppertsi:intowhichtheclay or other ceramic material tobe workedor pugged is dumped.Extendin'gi longitudinally 'throug-h the 'hopper isa mixing 1 shaft :14carrying, within -'-the hopper, a plurality of substantiallyradialarmsor blades 5 iorimixingsand tmascerating 'the' clay introducedinto?thezhopper'and feeding-it forward' to an 'upper: auger-' 6: alsoattached to the shaft .4.

The inner end of thesha it is mounted 1 within a casing or the like 1housing suitable gearing (not shown) driven by a variable speed motor-ofthe usual'type (not shown) for imparting' rotation to theshait'over-a-nyde'sird range of speeds. The shaft preferably extendscontinuously to the front walll'8'of the machine and 'is'rotatablysupported at itsiront end by a suitable bearin'gfl mounted in: the-wall.I

The upper-ormiXingauger-G ispinned or otherwisesecured to the s-haft' l.Thisauger has-a single continuously extending "helical vane or bladeill, 'thediameter ofwhich progressively decreases toward its -forwardend. The forepart'oi the mixing chamber ln which the auger is'housedisformed as a tubular casing or housing "I! of frusto-oonicalconfiguration which progressively effectively seal both openings andthus prevent air from being drawn into the chamber when suction isapplied.

From the vacuum the clay is fed into the extrusion device or outletportion of the pug mill. Forming a part of this device is a lower orextruding auger H which extrudes the clay from the mill and the innerend of which is arranged within the lower portion of the vacuum chamberin substantially vertical alignment with the shaft 4. The forward end ofthis auger is housed within a cylindrical casing or extrusion chamberwhich is preferably provided with a water-cooled jacket "5. Bolted orotherwise secured to the forward end of the casing is a nozzle or die I!of truncated cone-shape through which the clay is discharged from themill.

The extruding auger I4 is formed with a shaft or hub portion l8- whichis removably splined or otherwise keyed to an aligned with a drive shaft19, as by inwardly projecting ribs 2|. At its forward end the shaft l9isrotatably journaled in the rear wall of the vacuum chamber throughsuitable bearings. The rear end of the shaft l9 extends into and isjournaled within the casing 1. As in the case of the shaft 4, the shaft19 is adapted to be driven through suitable gearing (not shown) by avariable speed motor of the usual type (not shown), separate motorsbeing provided for the two shafts to enable their relathreaded into theend of the shaft IS.

The shredded clay forced into the vacuum chamber l3 by the upper auger 6is driven down toward the lower auger l4 by a pair of laterally spacedpaddles or the like 26. These paddles may be mounted on the forward endsof the shafts 21, the rear ends of which extend into the casing I andare there connected to a suitable source ofpower (not shown) throughwhich the desired rotation is transmitted to the paddles. The paddlesare preferably connected through suitable gearing (not shown) to asingle source of power, the latter desirably being a variable speedmotor of the usual type (not shown) to enablethe speed of the paddlesrelative to the mixing and extrusion augers to be controlled at will.

As described in my aforementioned co-pending application, Serial No.499,676, the extruding augeris provided with a plurality of spaced setsof flat blades 28, the radii of rotation of which are substantiallyequal to the-inner radius of the extrusionchamber [5. Each of thebladeslies normally to the axis of theshaftglB of the auger and within eachset the blades are diagonally or obliquely disposed such that each liesin a plane intersecting the other blades of the set. Additionally, theblades of each set are positioned to interrupt the flights of the bladesof the next preceding set. In each set, with the exception of theoutermost set, the trailing edge a of each blade is spaced laterallyfrom and in advance of the leading edge I) of the next adjacent blade ofits set. In the outermost set the trailing and leading edges, a and b,respectively, of the adjacent blades overlap in part.

Utilizing an extruding auger of the above construction, the clayextruded from the pug mill is driven at a substantially uniform speedthroughout the free area of the extrusion chamber. At the same time anylines of force or cleavage set up in the clay by'the flights of theblades of each set are cut or interrupted by the blades of the nextsucceeding set such that the clay, as extruded, is in substantiallystress-free condition. By enlarged the leading and trailing edges of theblades of the outermost set the clay is prevented from backing up intothe extrusion chamber.

As previously mentioned, the apparatus of the present invention isdesigned to handle ceramic materials or clays of different consistenciesand is particularly adapted to handle clays in which the moisturecontent is controlled. Accordingly, instead of utilizing the usualfilter cake as the starting material, there is preferably employed, thecontrolled moisture content mixture of my aforementioned co-pendingapplication, Serial No. 708,455. As therein described,- the startingmaterial is a bone-dry ceramic mixture. As preferred, water may be addedto this mixture either immediately preceding or as the mixture isintroduced into the hopper 3, in the latter case by such means as adispenser indicated at: 29 in Figure 1. In either case a measuredquantity of water relative to the weight of-the clay is added, the exactquantity depending on the consistency desired in the clay as extrudedfrom the mill. The ceramic materials and added water are then thoroughlymixed by both the paddles 5 and the mixing auger blade it into a mass ofhomogeneous moisture content which, after shredding by the member I2, isfed into the vacuum chamber l 3. Utilizing the variable speed motor,previously described, the speed at which the materials are mixed and fedforward by the mixing auger l0 will be controlled depending upon theamount present and its consistency. After,

entering the vacuum chamber the ceramic mixture or clay is freed of itsentrapped air and driven downwardly by the paddles 26 at the speedrequired to keep the mouth or entrance ofthe extrusion chamber filledand the vacuum chamber sealed against the entrance of outside air, thepaddles also serving to agitate the clay and expose a maximum of itssurface to the vacuum. Thereafter, the clay is driven through theextrusion chamber and extruded from the mill by the extruding auger I4,the speed of the latter being at varying speeds determined by itsquantity and consistency, ,it is possible to -obtain from start= ingmaterials of diiierent consistencies an extruded mass or pug which isboth stress-free and homogeneous. Thereby, the use of different mills aswell as the high percentage of losses, under present practice in thesubsequent drying and firing stages as the result of non-control ofthese factors, are practically eliminated.

It will be apparent from the above detailed description that there hasbeen provided an improved apparatus for mixing clay which, whileparticularly suited for the production of ceramic insulators, is of wideapplication in clay mixing. It should be understood that the describedand disclosed apparatus is merely exemplary of the invention and thatall modifications are intended to be included which do not depart eitherfrom the spirit of the invention or the scope of the appended claims.

I claim:

1. A pug mill adapted to handle ceramic materials of different moistureconsistency whereby so-called soft pugs and hard pugs can be obtainedfrom the same pug mill, said pug mill comprising a mixing chamber, avacuum chamber, and an extrusion chamber, said respective chambers beingconnected in serial relation whereby material fed into said mixingchamber will be discharged from said extrusion chamber, a mixing augerpositioned in said mixing chamber, means positioned in said vacuumchamber for impelling material therefrom into said extrusion chamber, anextrusion auger positioned in said extrusion chamber, and a variablespeed drive means connected to each of said augers and the impellingmeans, there being an independent drive means for each of said augersand the impelling means whereby any one of said augers or the impellingmeans may be driven at a predetermined rate of speed as desired, therelative rates of speed of said auger drives and the impelling meansdrive being determined in accordance with the consistency of the ceramicmaterials fed into said mixing chamber to permit discharge of saidmaterials from said extrusion chamber without breaking the vacuum in thevacuum chamber.

2. A pug mill adapted to handle ceramic materials of different moistureconsistency whereby so-called soft pugs and hard pugs can be obtainedfrom the same pug mill, said pug mill comprising a mixing chamber, avacuum chamber, and an extrusion chamber, said respective chambers beingconnected in serial relation whereby material fed into said mixingchamber will be discharged from said extrusion chamber, a mixing augerpositioned in said mixing chamber, an extrusion auger positioned in saidextrusion chamber, a paddle positioned in said vacuum chamber forimpelling material from said vacuum chamber into said extrusion chamber,and a variable speed drive means connected to each of said augers andthe paddle, there being an independent drive means for each of saidaugers and the paddle whereby said augers and paddle may be driven atindependent rates of speed, said rates of speed being determined inaccordance with the consistency of the material fed into the mixingchamber to permit discharge of said material from the extrusion chamberwithout breaking the vacuum in the vacuum chamber.

3. A pug mill adapted to handle ceramic materials of difierent moistureconsistency whereby so-called soft pugs and hard pugs can be obtainedfrom the same pug mill, said pug mill comprising a mixing chamber havinga discharge opening, a vacuum chamber having an inlet opening and adischarge opening, and an extrusion chamber having an inlet opening,means connecting said vacuum chamber to said mixing chamber whereby theinlet opening of said vacuum chamber is positioned in registry with thedischarge opening of said mixing chamber, means connecting saidextrusion chamber to said vacuum chamber whereby the inlet opening orsaid extrusion chamber is positioned in registry with the dischargeopening of said vacuum chamber, means positioned in said mixing chamberto feed material into the inlet opening of said vacuum chamber to keepsaid opening filled, means positioned in said vacuum chamber to forcematerial therefrom into the inlet opening of said extrusion chamber tokeep said opening filled and thus prevent loss of vacuum, and means tofeed material through said extrusion chamber, said mixing chamber feedmeans, vacuum chamber forcing means, and extrusion chamber feed meanseach having connected thereto an independent variable speed drive meanswhereby, depending upon the consistency of the material fed into saidmixing chamber, the rate of feed of said material through the pug millcan be adjusted so that vacuum is maintained in said vacuum chamber.

4. A pug mill adapted to handle ceramic materials of different moistureconsistency whereby so-called soft pugs and hard pugs can be obtainedfrom the same pug mill, said pug mill comprising an elongated mixingchamber having a discharge opening at one end thereof, a mixing augerpositioned axially of said chamber, a shredder connected to said mixingauger and positioned at the discharge opening of said mixing chamber, avacuum chamber positioned in extension of said mixing chamber, saidvacuum chamber having an inlet opening positioned in registry with thedischarge opening of said mixing chamber, means connecting saidrespective openings, said vacuum chamber also having a discharge openingpositioned substantially at right angles to the inlet opening of thevacuum chamber and opening downward from the vacuum chamber, a pluralityof paddles positioned in said vacuum chamber, said paddles beingconstructed and arranged to impel material within said vacuum chambertoward the discharge opening thereof, an extrusion chamber having aninlet opening positioned below and in registry with the dischargeopening of said vacuum chamber, an extrusion auger positioned in saidextrusion chamber and adapted to force material from the inlet openingof said extrusion chamber, and variable speed drive means connected tosaid paddles whereby said paddles may be driven at a rate of speedsufficient to keep the discharge opening of said vacuum chamber filledand thus prevent loss of vacuum in said vacuum chamber.

EDWARD M. SKIPPER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,614,526 Lambie et a1. Jan. 18,1927 1,879,367 Lotz i Sept. 27, 1932 1,987,358 Bonnot Jan. 8, 19351,987,359 Brown Jan. 8, 1935

